The present invention is applicable to a variety of writing instruments such as a fountain pen, a fabric-tip pen, a ball-point pen or the like, but is especially most effective when incorporated in writing instruments such as a fabric-pen and a water-ink ball-point pen.
The applicant has already filed applications on various writing instruments in which a seal cap or a seal ball is movable into and out of a sealing position in response to a knocking or turning motion for sealing a writing tip or unsealing the same in readiness for writing as disclosed by U.S. patent application No. 394,987 filed on July 2, 1982 by the present applicants, now U.S. Pat. No. 4,479,732 and U.S. patent application Ser. No. 394,957 filed on July 2, 1982 by the present applicants, now U.S. Pat. No. 4,469,462. These prior writing instruments have an air vent hole defined in the vicinity of a tip end portion of a cartridge to seal the writing tip near the tip end portion. This structural limitation prevents such prior arrangements from being incorporated in writing members or ink cartridges generally available on the market or those with small modifications. Therefore, the prior inventions have required ink cartridges to be constructed as a whole with special design.